Where inflatable packers are used to isolate a well interval to be tested, it is fairly common practice to use a downhole pump that is operated in response to rotation of the pipe string on which the test tools are suspended. The housing of the pump is coupled to drag springs or the like which engage the well bore wall to prevent rotation of the housing, and a mandrel assembly that extends into the housing is rotated relative thereto to cause pump piston reciprocation via a rotary-to-reciprocating motion converter.
There is always the risk in drill stem testing that the packer elements can become stuck in the well for a variety of reasons. For example, a damaged rubber element may wedge the tool in the hole, or differential pressure sticking can occur. Should this happen, it is desirable to be able to remove as much of the downhole tool string as possible before the stuck tools are washed over. For this purpose, it is fairly typical practice to include a safety joint located just above the upper packer element which can be backed off in response to manipulation of the pipe so as to intentionally part the tool string at that point. Since the mandrel and housing assembly of a rotary pump must necessarily provide a freely rotatable joint, the operation of a safety joint located therebelow can be a problem for apparent reasons. It is to a unique solution to this problem that the present invention is directed.
A general object of the present invention is to provide a new and improved rotary operated downhole pump assembly of the type described where the mandrel can be freely rotated relative to the housing only in the hand direction (usually right) normally used to actuate the pump.
Another object of the present invention is to provide a new and improved rotary operated downhole pump assembly of the type described that includes a clutch mechanism which allows free right-hand rotation of the mandrel relative to the housing but which engages in response to left-hand rotation to force the housing to rotate with the mandrel and cause back-off at a safety joint included in the tool string therebelow.